flam·ma·ble

flammable

Flammable and inflammable sound like they are antonyms, or opposites. In fact, they are synonyms, words that have the same meaning. Both flammable and inflammable mean "quick to catch fire and burn." You might see either word printed on a warning sign on a tank truck. If you want to describe something that is slow or not able to catch fire and burn, try "not flammable" or "fire-resistant."